BIOLOGY · Stage 8 · Chapter 7: The Health of the Environment
Biology 7.5 Invasive species — Ecological Competition — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Lesson summary
7.5 Invasive species — Ecological Competition — Alhussan International Academy — Biology (Stages 7–9) notes: Distinguish native, introduced and invasive species, and explain how invasive species compete with native organisms and reduce biodiversity.Native species = species that a…
- Introduced (non-native) species
- No natural predators
- Rapid breeding
- Broken food webs
- Why invaders win
- Native range
Section 1 of 7Native, introduced and invasive species
1Native species1 point
= species that are a natural part of an ecosystem.
- Tree ferns in New Zealand, hummingbirds in the Caribbean and silver-studded blue butterflies in Western Europe are examples.
2Introduced (non-native) species1 point
= species brought into an ecosystem by human activity.
- Many do not upset the balance and some even have a positive effect, such as pheasants introduced into Europe by the Romans.
3Invasive species2 points
= an animal or plant introduced by humans that spreads quickly and damages the ecosystem, economy or health.
- They may be introduced deliberately, for food or because they look nice, or arrive accidentally.
- Not every introduced species is invasive.
Section 2 of 7Why invasive species are a problem
- No natural predators
- a new species often has no predators or diseases in its new area to limit its numbers.
- Rapid breeding
- invasive species usually reproduce quickly, so the population grows fast.
- Broken food webs
- they quickly affect other organisms and break existing food chains and webs.
Section 3 of 7Competition
- Competition
- organisms compete when they need the same limited resource.
- Animals compete for food, water, mates and territory.
- Plants compete for light, water and mineral ions.
- Outcome
- the better adapted species usually survives and reproduces more, and the other declines.
- Why invaders win
- an invasive species may grow faster, eat a wider range of food or reproduce more quickly than native species.
Section 4 of 7Cane toads
- Diet
- cane toads are big and eat rats, mice, reptiles, amphibians, birds, insects and even bats.
- Native range
- in South and Central America they are eaten by caiman, snakes, large fish and ibis.
- Introduction
- they were introduced to many countries to control pests.
- Their skin is toxic, so in the new countries they have no predators and became pests themselves.
- They eat large numbers of native species, break down food webs and drove species such as the northern quoll of Australia to the edge of extinction.
Section 5 of 7Water hyacinth
1Origin2 points
- it is a floating plant from South America and one of the fastest growing plants known.
- It was spread to Africa, Asia, Europe, the Middle East and the USA because of its pink ornamental flowers.
2Damage3 points
- it covers lakes and waterways in a thick mat.
- It absorbs lots of water and blocks sunlight and oxygen from the water beneath.
- Other water plants, invertebrates and fish die, and ecosystems have been destroyed from Sri Lanka and Nigeria to Iraq.
3Responses3 points
- chemical pesticides, physical removal and biological control by introducing animals that eat the plant.
- None has removed the plant completely.
- In India farmers dry the plants for fuel and use the ash as fertiliser, and others ferment them to make methane gas for fuel.
Section 6 of 7Effects on ecosystems
- Native species may decline or become extinct, so biodiversity is reduced.
- Food webs are altered because a new predator or competitor changes populations at several levels.
- Crops, livestock and fisheries can be harmed, which costs money.
- Native species may have no defence against a new disease, such as the squirrel pox virus carried by grey squirrels, which harms red squirrels.
- Other examples
- rabbits in Australia and grey squirrels in the UK.
Section 7 of 7Why the effect is so large
| Feature | Native species | Invasive species |
|---|---|---|
| Limited by predators and disease | Yes | Often none, so numbers rise quickly |
| Adapted to local conditions | Yes | May be better at using resources |
| Population balance | Balanced | Can upset the balance and dominate |
- Prevention
- checking cargo and ballast water is far cheaper than removing a species once it has spread.
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